Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates a substrate designed to improve light extraction efficiency from a semiconductor light emitting device, described in more detail in US 2013/0015487. On the sapphire substrate 10, a plurality of grooves 11 extending in a first direction (along the x-axis) is formed in a parallel stripe pattern. The remaining ungrooved surface is a top surface 10a of the substrate. The width of each groove 11 is 1.5 μm in the y-axis direction, and the width of each stripe of ungrooved portion 10a in the y-axis direction is 1.5 μm in the y-axis direction. The depth of each groove 11 is 0.1 μm. The depth of each groove 11 may be within a range from 100 Å to 3 μm.
A plurality of SiO2 dielectric stripes 15 are formed in parallel on the bottom surfaces and side surfaces of the grooves 11, and on the surface 10a of the sapphire substrate 10. Each dielectric stripe 15 extends in a second direction (y-axis direction). The width of each dielectric stripe 15 is 1.5 μm in the x-axis direction. The thickness of each dielectric stripe 15 may be within a range of 100 Å to 1 μm. On the sapphire substrate 10 having the configuration shown in FIG. 1, an aluminum nitride (AlN) buffer layer having a film thickness of 10 nm is deposited. The buffer layer (not shown in FIG. 1) is formed over the bottom surfaces 11a and side surfaces 11b of the grooves 11, the surface 10a, and the top surfaces 15a and the side surface 15b of the dielectric stripes 15.